The present invention relates to a sealing device for an extruder for the evacuation of air, the extruder including a cylinder with a die and a reciprocating piston.
In the production of longitudinal metal sections by the traditional method, a shaping machine of the above type is used. A metal billet with a circular cross-section is preheated and placed in the cylinder. Then the piston presses the billet through the die with great force. The extrusions thus formed take on different shapes depending on the shape of the hole in the die.
Work is being done to develop methods of producing metal sections based on the use of particulate material such as metal powder or needles. However, when one uses particulate material to make a bolt or metal extrusion, there are increased problems with air pockets and moisture, and this detracts form the quality of the extrusion.
EP Patent Application No. 0397423 describes a method and equipment for producing metal objects by consolidation of particulate material, using an extruder with a solution for the evacuation of gas. A piston is used with a wedge, where the gas is sucked out past the wedge and through a bore in the piston. This solution gives an end product which is very close to optimum, i.e. which to all intents and purposes is without deleterious impurities and pores, and which has an almost impermeable surface which prevents absorption of humidity and gas during later use. However, there is one disadvantage with such equipment, i.e. that it does not achieve a satisfactory seal between the piston and the cylinder, and this in turn means that air is drawn into the cylinder during the extraction operation when a strong vacuum is used.
Also known is an extruder where air is extracted from the extruder cylinder by means of a venting plate which is pressed against a venting ring mounted on the cylinder. The venting plate can be moved by means of piston/cylinder mechanisms. This solution is complicated and costly. In addition, it requires a great deal of space and would obstruct the movements of anyone operating it.